Roll-to-roll metallization of solar cells

ABSTRACT

Disclosed herein are approaches to fabricating solar cells, solar cell strings and solar modules using roll-to-roll foil-based metallization approaches. Methods disclosed herein can comprise the steps of providing at least one solar cell wafer on a first roll unit and conveying a metal foil to the first roll unit. The metal foil can be coupled to the solar cell wafer on the first roll unit to produce a unified pairing of the metal foil and the solar cell wafer. We disclose solar energy collection devices and manufacturing methods thereof enabling reduction of manufacturing costs due to simplification of the manufacturing process by a high throughput foil metallization process.

BACKGROUND

Photovoltaic (PV) cells, commonly known as solar cells are well knowndevices for direct conversion of solar radiation into electrical energy.Generally, solar cells are fabricated on a semiconductor wafer orsubstrate using semiconductor processing techniques to form a p-njunction near a surface of the wafer. Solar radiation impinging on thesurface of, and entering into, the wafer creates electron and hole pairsin the bulk of the wafer. The electron and hole pairs migrate to p-dopedand n-doped regions in the wafer, thereby generating a voltagedifferential between the doped regions. The doped regions are connectedto conductive regions on the solar cell to direct an electrical currentfrom the cell to an external circuit coupled thereto.

Efficiency is an important characteristic of a solar cell as it isdirectly related to the capability of the solar cell to generate power.Likewise, efficiency in producing solar cells is directly related to thecost effectiveness of such solar cells. Accordingly, techniques forincreasing the efficiency of solar cells, or techniques for increasingthe efficiency in the manufacture of solar cells, are generallydesirable. Some embodiments of the present disclosure allow forincreased solar cell manufacture efficiency by providing novel processesfor fabricating solar cell structures.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings illustrate b way of example and not limitation.For the sake of brevity and clarity, every feature of a given structureis not always labeled in every figure in which that structure appears.Identical reference numbers do not necessarily indicate an identicalstructure. Rather, the same reference number may be used to indicate asimilar feature or a feature with similar functionality, as maynon-identical reference numbers. The figures are not drawn to scale.

FIG. 1 depicts operations in a method of fabricating a solar cell orsolar cell string, in accordance with an embodiment of the presentdisclosure;

FIG. 2 depicts a method of fabricating a solar cell or solar cellstring, in accordance with an embodiment of the present disclosure;

FIG. 3A and FIG. 3B depicts solar cells, in accordance with anembodiment of the present disclosure;

FIG. 4 depicts operations in a method of fabricating a solar cell stringor solar module, in accordance with an embodiment of the presentdisclosure;

FIG. 5 depicts a method of fabricating a solar cell string or solarnodule, in accordance with an embodiment of the present disclosure;

FIG. 6 depicts a method of fabricating a solar cell string or solarmodule, in accordance with an embodiment of the present disclosure;

FIG. 7 depicts a method of fabricating a solar cell string or solarmodule, in accordance with an embodiment of the present disclosure;

FIG. 8 depicts a solar cell string, in accordance with an embodiment ofthe present disclosure;

FIG. 9 depicts a solar module, in accordance with an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter of theapplication or uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

Certain terminology may be used in the following description for thepurpose of reference only, and thus are not intended to be limiting. Forexample, terms such as “upper”, “lower”, “above”, and “below” refer todirections in the drawings to which reference is made. Terms such as“front”, “back”, “rear”, “side”, “axial”, and “lateral” describe theorientation and/or location of portions of the component within aconsistent but arbitrary frame of reference which is made clear byreference to the text and the associated drawings describing thecomponent under discussion. Such terminology may include the wordsspecifically mentioned above, derivatives thereof, and words of similarimport. Similarly, the terms “first”, “second”, and other such numericalterms referring to, structures do not imply a sequence or order unlessclearly indicated by the context.

Terminology—The following paragraphs provide definitions and/or contextfor terms found in this disclosure (including the appended claims):

This specification includes references to “one embodiment” or “anembodiment.” The appearances of the phrases “in one embodiment” or “inan embodiment” do not necessarily refer to the same embodiment.Particular features, structures, or characteristics can be combined inany suitable manner consistent with this disclosure.

This term “comprising” is open-ended. As used in the appended claims,this term does not foreclose additional structure or steps.

Various units or components may be described or claimed as “configuredto” perform a task or tasks. In such contexts, “configured to” is usedto connote structure by indicating that the units components includestructure that performs those task or tasks during operation. As such,the unit/component can be said to be configured to perform the task evenwhen the specified unit/component is not currently operational (e.g., isnot on/active). Reciting that a unit/circuit/component is “configuredto” perform one or more tasks is expressly intended not to invoke 35U.S.C. § 11.2, sixth paragraph, for that unit/component.

As used herein, the terms “first,” “second,” etc. are used as labels fornouns that they precede, and do not imply any type of ordering (e.g.,spatial, temporal, logical, etc.). For example, reference to a “first”encapsulant layer does not necessarily imply that this encapsulant layeris the first encapsulant layer in a sequence; instead the term “first”is used to differentiate this encapsulant from another encapsulant(e.g., a “second” encapsulant.).

The terms “a” and “an” are defined as one or more unless this disclosureexplicitly requires otherwise.

The following description refers to elements or nodes or features being“coupled” together. As used herein, unless expressly stated otherwise,“coupled” means that one element/node/feature is directly or indirectlyjoined to (or directly or indirectly communicates with) anotherelement/node/feature, and not necessarily mechanically.

As used herein, “inhibit” is used to describe a reducing or minimizingeffect. When a component or feature is described as inhibiting anaction, motion, or condition it may completely prevent the result oroutcome or future state completely. Additionally, “inhibit” can alsorefer to a reduction or lessening of the outcome, performance, and/oreffect which might otherwise occur. Accordingly, when a component,element, or feature is referred to as inhibiting a result or state, itneed not completely prevent or eliminate the result or state.

As used herein, the term “substantially” is defined as largely but notnecessarily wholly what is specified (and includes what is specified;e.g., substantially 90 degrees includes 90 degrees and substantiallyparallel includes parallel), as understood by a person of ordinary skillin the art. In any disclosed embodiment, the terms “substantially,”“approximately,” and “about” may be substituted with “within [apercentage] of” what is specified, where the percentage includes 0.1, 1,5, and 10 percent.

As used herein “regions” can be used to describe discrete areas,volumes, divisions or locations of an object or material havingdefinable characteristics but not always fixed boundaries.

In the following description, numerous specific details are set forth,such as specific operations, in order to provide a thoroughunderstanding of embodiments of the present disclosure. It will beapparent to one skilled in the art that embodiments of the presentdisclosure may be practiced without these specific details. In otherinstances, well-known techniques are not described in detail in order tonot unnecessarily obscure embodiments of the present invention. Thefeature or features of one embodiment can be applied to otherembodiments, even though not described or illustrated, unless expresslyprohibited by this disclosure or the nature of the embodiments.

Although many of the examples described herein are back contact solarcells, the techniques and structures apply equally to other (e.g., frontcontact) solar cells as well. Moreover, although much of the disclosureis described in terms of solar cells, the disclosed techniques andstructures apply equally to other semiconductor structures (e.g.,silicon wafers, or large area light emitting diodes, or substratesgenerally).

Methods of fabricating solar cells using roll-to-roll foil-basedmetallization approaches, and the resulting solar cells, are describedherein. In the following description, numerous specific details are setforth, such as specific process flow operations, in order to provide athorough understanding of embodiments of the present disclosure. It willbe apparent to one skilled in the art that embodiments of the presentdisclosure may be practiced without these specific details. In otherinstances, well-known fabrication techniques are not described in detailin order to not unnecessarily obscure embodiments of the presentdisclosure. Furthermore, it is to be understood that the variousembodiments shown in the figures are illustrative representations andare not necessarily drawn to scale.

Disclosed herein are methods of fabricating solar cells, solar cellstrings and solar modules. In one embodiment, a method of fabricating asolar cell includes providing at least one wafer or substrate on a firstroll unit. In an embodiment, a silicon substrate of a solar cell isprovided on the first roll unit. The solar cell can comprise a pluralityof semiconductor regions in and/or above the wafer or substrate. Themethod further comprises a step of conveying a metal foil to the firstroll unit. The metal foil contacts the wafer of a solar cell on thefirst roll unit. Additionally, the method comprises the step of couplingthe metal foil to the wafer to provide a unified pairing of the metalfoil and the wafer to form a metallized solar cell.

Also disclosed herein are solar cells, solar cell strings and solarmodules fabricated in a roll-to-roll foil-based metallization approach.In an embodiment, a solar cell includes a wafer or substrate. In anembodiment, a plurality of semiconductor regions are disposed in and/orabove the substrate. The solar cell comprises a patterned metal foilcoupled to the wafer. In an embodiment, the patterned metal foilcomprises electrically isolated regions corresponding to and/or inalignment with the plurality of semiconductor regions.

One or more embodiments described herein provide for roll-to-rollfoil-based metallization approaches. Advantages include reduction of thecost of manufacturing a solar cells, strings and modules due tosimplification of the manufacturing process by a high throughput foilmetallization process. The roll-to-roll foil-based metallizationapproaches described herein enable low cost and efficient solar cellmetallization without electroplating.

FIG. 1 depicts a flowchart 100 listing operations in a method offabricating a solar cell, in accordance with an embodiment of thepresent disclosure. Referring to operation 102 of flowchart 100 and tocorresponding FIG. 2, a method of fabricating a solar cell or solar cellstring comprises providing at least one wafer of a solar cell 112 on afirst roll unit 120. The first roll unit 120 rotates the solar cellwafers 112 along a first conveyance path generally depicted at 122. Forease of description, individual wafers at particular positions along thefirst roll unit 120 are indicated by 112 a, 112 b and 112 n.

In one embodiment, each wafer of a solar cell 112 comprises amonocrystalline silicon substrate. For example, wafer of solar cell 112comprises an n-type or a p-type monocrystalline silicon substrate. Inother embodiments, wafer of solar cell 112 comprises an n-type or ap-type multi-crystalline silicon substrate. In yet other embodiments,wafer of solar cell 112 comprises an amorphous silicon substrate. In oneembodiment, the thickness of the wafer is less than 300 μm. As anotherexample, the thickness of the wafer is less than 150 μm. In someembodiments, the wafer thickness can be between 50-300 μm.

In an embodiment, each wafer of a solar cell 112 comprises a front side114 facing the sun during normal operation to collect solar radiationand a back side 116 opposite the front side. As depicted in FIG. 2, thefront sides 114 contact the first roll unit 120. In one embodiment, thesolar cell 112 is a back contact solar cell, however the techniques andstructures apply equally to other (e.g., front contact) solar cells aswell.

In an embodiment, each solar cell 112 comprises a plurality ofsemiconductor regions on and/or above a substrate. For example solarcells 112 can comprise alternating n-type and p-type polycrystallinesilicon semiconductor regions on and/or above a silicon substrate.

In some embodiments, a method of fabricating a solar cell includesforming a plurality of semiconductor regions in and/or above asubstrate. For example, FIG. 3A depicts solar cell wafer 112 accordingto one embodiment. Solar cell wafer 112 comprises a plurality ofsemiconductor regions 113/115 in and/or above substrate 111. In someembodiments, a thin dielectric material may be included as anintervening material between the semiconductor regions 113/115 and thesubstrate 111. The substrate 111 has a light-receiving surface 114opposite a back surface above which the plurality of semiconductorregions 113/115 is formed. In an embodiment, as depicted in FIG. 3A,each of the plurality of semiconductor regions 113/115 is spaced apartfrom one another. In a specific embodiment, the plurality ofsemiconductor regions 113/115 is a plurality of alternating n-type 113and p-type 115 semiconductor regions.

In an embodiment, the substrate 111 is a monocrystalline siliconsubstrate, such as a bulk single crystalline n-type doped siliconsubstrate. It is to be appreciated, however, that substrate 111 may be alayer, such as a multi-crystalline silicon layer, disposed on a globalsolar cell substrate. In at embodiment, the thin dielectric layer 117 isa tunneling silicon oxide layer having a thickness of approximately 2nanometers or less. In one such embodiment, the term “tunnelingdielectric layer” refers to a very thin dielectric layer, through whichelectrical conduction can be achieved. Not to be bound by any particulartheory, but the conduction may be due to quantum tunneling and/or thepresence of small regions of direct physical connection through thinspots in the dielectric layer. In one embodiment, the tunnelingdielectric layer is or includes a thin silicon oxide layer.

In an embodiment, in the case that the plurality of semiconductorregions 113/115 is a plurality of alternating n-type 113 and p-type 115semiconductor regions, the alternating n-type and p-type semiconductorregions 113 and 115, respectively, are polycrystalline silicon regionsformed by, e.g., using a plasma-enhanced chemical vapor deposition(PECVD) process. In one such embodiment, the n-type polycrystallinesilicon regions 113 are doped with an n-type impurity, such asphosphorus. The P-type polycrystalline silicon regions 204 are dopedwith a P-type impurity, such as boron. As is depicted in FIG. 3A, thealternating n-type and p-type semiconductor regions 113 and 115 may havetrenches 118 formed there between, the trenches 118 extending partiallyinto the substrate 111. In an embodiment, an insulating layer 119 isdisposed in the trenches 118 and between and partially on thealternating n-type and p-type semiconductor regions 113 and 115, as isdepicted in FIG. 3A. In some embodiments, a bottom anti-reflectivecoating (BARC) material or other protective layer (such as a layeramorphous silicon) is formed on the alternating n-type 113 and p-type115 semiconductor regions.

In an embodiment, the light receiving surface 114 is a texturized lightreceiving surface, as is depicted in FIG. 3A. In one embodiment, ahydroxide-based wet etchant is employed to texturize the light receivingsurface 114 of the substrate 111 and, possibly, the trench 118 surfacesas is also depicted in FIG. 3A. It is to be appreciated that the timingof the texturizing of the light receiving surface may vary. For example,the texturizing may be performed before or after the formation of thethin dielectric layer 117. In an embodiment, a texturized surface may beone which has a regular or an irregular shaped surface for scatteringincoming light, decreasing the amount of light reflected off of thelight receiving surface 114 of the solar cell. Referring again to FIG.3A, additional embodiments can include formation of a passivation and/oranti-reflective coating (ARC) layers (shown collectively as layer 212)on the light receiving surface 114. It is to be appreciated that thetiming of the formation of passivation and/or ARC layers may also vary.

In an embodiment, the plurality of semiconductor regions 113/115 isformed from a polycrystalline silicon layer formed above the substrate111, which may be a single or multi-crystalline silicon substrate, asdescribed above. In another embodiment, however, the substrate 111 is asingle crystalline silicon substrate having the plurality ofsemiconductor regions 113/115 formed therein, as opposed to being formedin a semiconductor layer distinct from the substrate 111.

A plurality of contact openings can be formed in insulating layer 119.The plurality of contact openings can provide exposure to the pluralityof n-type doped polysilicon regions 113 and to the plurality of p-typedoped polysilicon, regions 115. In one embodiment, the plurality ofcontact openings is formed by laser ablation. In one embodiment, thecontact openings to the n-type doped polysilicon regions 113 havesubstantially the same height as the contact openings to the p-typedoped polysilicon regions 115.

In an embodiment, the first roll unit 120 is an elongated cylindricaldevice comprising a circular cross-section such as depicted in FIG. 2.In other embodiments, the first roll unit comprises a plurality ofsubstantially planar surfaces sized to hold a single wafer of a solarcell. The first roll unit 120 can comprise any desirable material, forexample, metal, plastic, ceramic, graphite or a combination thereof. Thefirst roll unit 120 is configured to rotate about an axis and can bedriven by a motor providing power to the first roll unit 120. In oneembodiment, the motor provides power to steadily rotate the first rollunit 120. In other embodiments, the first roll unit 120 can rotateintermittently, or in an indexed manner. The magnitude of the indexingmotion of the first roll unit can be adjusted as desired. In someembodiments, a roll unit comprises a single roller; however in otherembodiments, a roll unit can comprises a plurality of rollers.

The diameter and width of the first roll unit can be of any desirabledimensions. In one embodiment, the first roll unit is sized to hold,support and/or maintain a plurality of wafers in a predetermined cellstring matrix or arrangement of a solar module. In several embodiments,the number of cells or length of a cell string is greater than thenumber of cells that are maintained on the first roll unit at any onetime. For example, a cell string can comprise 10 or more solar cellswith the first roll unit holding 9 cells at once as depicted in FIG. 2.

In an embodiment, the dimensions of the first roll unit are determinedbased on the dimensions of the wafers or solar cells. As a non-limitingexample, the wafers can be 12-16 cm in width. In one embodiment, the gapbetween adjacent cells in a solar cell string can be less than 2 mm. Inanother embodiment, the gap between adjacent cells in a solar cellstring can be less than 1 mm, for example approximately 0.5 mm.

In one embodiment, a wafer can be provided on the first roll 120 unitwhich is heated to a predetermined temperature. The first roll unit 120can transfer thermal energy to wafers 112 a-n in contact with the firstroll unit 120. In some embodiments, wafers 112 can be heated or“pre-heated” before coming into contact with the first roll unit 120.Any desirable heating mechanism can be employed, for example,conduction, convection, radiative e.g. infrared, and/or inductionheating.

Referring to operation 104 of flowchart 100 and to corresponding FIG. 2,a method of fabricating a solar cell or solar cell string comprisesconveying a metal foil 132 from a second roll unit 130 to the first rollunit 120 along a second conveyance path 122′. As depicted in FIG. 2, acontinuous length of the metal foil 132 is unrolled from the second rollunit 130 and transported along a second conveyance path 122′ to thefirst roll unit 120 to contact the back side 116 of wafer of solar cell112 n along the first conveyance path 122. As depicted, the secondconveyance path 122′ merges with the first conveyance path at theposition of solar cell 112 n. In some embodiments, a one or more guiderollers can be employed to guide the metal foil along a secondconveyance path 122′ from the second roll unit to the first roll unit.In various embodiments, foil 132 is heated to a predeterminedtemperature along the second conveyance path. In one embodiment, thefoil is heated at the second roll unit 130 heated to a predeterminedtemperature. Any desirable heating mechanism can be employed, forexample, conduction, convection, radiative e.g. infrared, and/orinduction heating.

In various embodiments, the metal foil 132 is an aluminum (Al) foilhaving a thickness less than 200 μm. As another example, the metal foilcan have a thickness approximately in the range of 5-100 microns. In oneembodiment, the metal foil is an aluminum alloy foil including aluminumand second element such as, but not limited to, copper, manganese,silicon, magnesium, zinc, tin, lithium, or combinations thereof. In oneembodiment, the aluminum foil is a temper grade foil such as, but notlimited to, F-grade (as fabricated), O-grade (full soft), H-grade(strain hardened) or T-grade (heat treated). In one embodiment, thealuminum foil is an anodized aluminum foil. In some embodiments, themetal foil is selected from the group of aluminum, copper, nickel,manganese, silicon, magnesium, zinc, tin, lithium, or combinationsthereof.

In an embodiment, the second roll unit is an elongated cylindricaldevice comprising a circular cross-section such as depicted in FIG. 2.As depicted, the second roll unit 130 is a roll of metal foil that iscontinuously unrolled and conveyed to the first roll unit 120 to contactthe wafer of solar cell 112 n. The second roll unit 130 can comprise anydesirable material, for example, metal, plastic, ceramic, graphite or acombination thereof. The second roll unit 130 is configured to rotateabout an axis and can be driven by a motor providing power to rotate thesecond roll unit 130. As it would become apparent to those skilled inthe art (e.g. web converting arts), the second roll unit can be rotatedin any desirable manner so as to maintain tension on the foil section132. For example, a clutch and counter rotation motor, or brake incombination with a tension measuring device, such as a ‘dancer’ rollercan be employed. Referring to operation 106 of flowchart 100 and tocorresponding FIG. 2, a method of fabricating a solar cell or solar cellstring comprises coupling the metal foil to the wafer to provide aunified pairing of the metal foil and the wafer, thereby forming ametallized solar cell or solar cell string. In one embodiment, the metalfoil is fixedly coupled or bonded to the back sides 116 of the wafer ofsolar cell 112 n by applying a mechanical force 140 directed towards thewafer 112 n on the first roller unit 120 as depicted in FIG. 2. Forexample a mechanical force 140 can be applied to a bonding head, abonding roller, a bonding plate or a bonding paddle directed towardssolar cell 112 n. In other embodiments, operation 106 comprises a laserwelding process wherein the metal foil 132 is coupled or bonded to thewafer 112 n by impinging a laser beam on the metal toil 132 to weld themetal foil to the wafer 112 n. In yet other embodiments, an ultrasonicbonding or welding process can be employed to couple the metal foil 132to the wafer 112 n. Any desirable mechanism can be used to bond themetal foil to the wafer. In one embodiment, the resulting bond can becharacterized as having an interface adhesion energy of greater than 4Joules/m².

In an embodiment, the metal foil is coupled to the wafer of solar cellat 112 n to produce a solar cell string 150 comprising a metal foilinterconnect between each of the plurality of solar cells. In someembodiments, step 106 comprises applying a force to the metal foil suchthat a shear force appears between the metal foil and the surface of thewafer to electrically connect a substantial portion of the metal foilwith the surface of the wafer. In some embodiments, the method comprisesa step of dispensing a conductive adhesive at the metal foilinterconnect between the plurality of cells.

In an embodiment, a parallel plate press of a metal foil by a flatbonding head onto the wafer may not produce an optimal bond between thewafer and the metal foil. Instead, although not to be bound by theory,in accordance with one or more embodiments described herein, applicationof first point force or pressure and then a shear force or pressure atstep 106 can provide for improved coupling or bonding. Not to be boundby any particular theory, but this approach allows the metal foil tolocally stretch at the interface, in some instances breaking apassivating oxide and allowing the metal foil to “stick” to theunderlying wafer.

In various embodiments, the plurality of wafers are heated to apredetermined temperature before and/or during step 102 and/or 106 offlowchart 100. In one embodiment, a wafer can be provided on the firstroll 120 unit which is heated to a predetermined temperature. The firstroll unit 120 can transfer thermal energy to wafers 112 a-n in contactwith the first roll unit 120. In some embodiments, wafers 112 can beheated or “pre-heated” before coming into contact with the first rollunit 120. Any desirable heating mechanism can be employed, for example,conduction, convection, radiative e.g. infrared, and/or inductionheating.

In various embodiments, the metal foil 132 is heated to a predeterminedtemperature before and/or during step 104 and/or step 106 of flowchart100. In one embodiment, the metal foil 132 can be heated before orduring conveying the metal foil 132 to the first roll unit 120. Forexample, the second roll unit 130 can transfer thermal energy to themetal foil 132. In some embodiments, the metal foil 132 can be heated inthe process of being conveyed to the first roll unit 120.

In several embodiments, solar cell 112 n and/or the metal foil 132 areheated to a predetermined temperature during the step 106 of couplingthe metal foil to the solar cell 112 n. In an embodiment, the solar cell112 n and the metal foil 132 are heated to a predetermined bondingtemperature during the coupling or bonding step 106. For example, amechanical force 140 can be applied to a heated bonding head, a heatedbonding roller, a heated bonding plate or a heated bonding paddledirected towards solar cell 112 n. As described above, the first rollunit 120 can be heated so as to conduct heat to the wafer and/for foil.

The wafer of the solar cell and/or the metal foil as well as the rollunits can be heated to any desired temperature. In some embodiments, thepredetermined temperature can be approximately in the range of 100-600°C. As another example, the predetermined temperature can beapproximately in the range of 350-580° C.

FIG. 1 and FIG. 2 illustrate approaches to fabricating solar cells usingroll-to-roll foil-based metallization according to one embodiment.Unless otherwise designated, the steps and components of FIG. 4-9 aresimilar, except that they have been incremented sequentially by 100.

FIG. 4 depicts a flowchart 200 listing operations in a method offabricating a solar cell string or solar module, in accordance with anembodiment of the present disclosure. Optional operations of flowchart200 are indicated by dashed lines. Referring to operation 202 offlowchart 200 and to corresponding FIG. 5, a method of fabricating asolar cell string or solar module comprises providing a plurality ofsolar cells 212 on a first roll unit 220. The first roll unit 220rotates the solar cells 212 along a first conveyance path generallydepicted at 222.

In one embodiment, the first roll unit comprises a plurality ofsubstantially planar surfaces sized to maintain, hold or support asingle wafer of a solar cell. For example, the first roll unit 220comprises eight substantially planar surfaces defining an octagonalcross-section, however any desirable number of substantially planarsurfaces in any desirable configuration can be employed. As depicted inFIG. 5, each substantially planar surface of first roll unit 220 issized to hold a single wafer of a solar cell 212. In other embodiments,a substantially planar surface of a first roll unit can be sized to holda plurality of wafers in any desirable configuration. The first rollunit 220 is configured to rotate (e.g. clockwise as depicted in FIG. 5)about an axis to transport the solar cells 212 along the firstconveyance path 222.

In an embodiment, the first roll unit can maintain, hold or supportwafers by any desirable gripping, grasping, or releaseably couplingdevice or technique. For example, directing a stream of gas towards thecell, a gripping mechanism with electro-mechanical grasping elementsand/or a vacuum interface for holding an object against itself can beused. In some embodiments, providing a wafer on the first roll unitcomprises applying a vacuum suction to hold a wafer on the first rollunit, wherein the first roll unit comprises conduits or tunnels forevacuating air to produce a vacuum suction through the conduit ortunnel; thereby holding a wafer of a solar cell in place while on thefirst roll unit.

Referring to operation 204 of flowchart 200 and to corresponding FIG. 5,a method of fabricating a solar cell string or module comprisesconveying a metal foil 232 from a second roll unit 230 to the first rollunit 220. As depicted in FIG. 2, a continuous length of the metal foil232 is unrolled from the second roll unit 230 and transported to thefirst roll unit 220 to contact solar cells 212 being transported alongthe first conveyance path 222. As depicted, the second conveyance path222′ merges with the first conveyance path at the position of solar cell212 n. A plurality of guide rollers 234 unit can be, employed to guidethe metal foil 232 along the second conveyance path 222′ from the secondroll unit 230 to the first roll unit 220. In an embodiment, the metalfoil 232 is tensioned or stretched at an angle on a corner or edge 235between two substantially planar sections of the first roll unit 220 asdepicted in FIG. 6. The edge 235 can constrain the foil 235, therebyvoiding formation of out-of-plane undulations. Any suitable mechanismand/or structure can be used to prevent wrinkles from forming in thefoil a232 before being coupled to the wafer 212 n.

Referring to operation 206 of flowchart 100 and to corresponding FIG. 5,a method of fabricating a solar cell string or module comprises couplingthe metal foil 232 to the wafer of a solar cell at position 212 n toprovide a unified pairing of the metal foil 232 and the wafer 212 n. Atstep 206, the metal foil 232 can be coupled to the plurality of solarcells 212 to produce a solar cell string 250 comprising a metal foilinterconnect between each of the plurality of solar cells 212. In oneembodiment, the metal foil 232 is fixedly coupled to solar cell 212 n byapplying a mechanical force directed towards the first roller unit 220.In one embodiment, a parallel plate press of the metal foil 232 by aflat bonding head is applied to wafer 212 n. In other embodiments, abonding roller can roll across the surface of the metal foil 232 whileapplying a force directed towards first roll unit 220, thereby bondingmetal foil 232 to wafer of solar cell 212 n.

Not to be bound by any particular theory, but a parallel plate press maynot produce an optimal bond between the wafer and the metal foil.Instead, in accordance with one or more embodiments described herein,application of first point force or pressure and then a shear force orpressure at step 206 can provide for improved coupling or bonding. Notto be bound by any particular theory, but this approach allows the metalfoil to locally stretch at the interface, in some instances breaking apassivating oxide and allowing the metal foil to “stick” to theunderlying wafer.

As depicted in FIG. 5, a mechanical force is applied to the solar cell212 n by a bonding head 242 comprising a bonding roller 244. The bondinghead is configured to direct the bonding roller against solar cell 212 nalong the direction indicated by 246. In various embodiments, thedirection of the bonding head or roller can be in a direction oppositeor perpendicular to direction 246 depending on the desired couplingmechanism and/or configuration.

In several embodiments, solar cell 212 n and/or the metal foil 232 areheated to a predetermined temperature during coupling the metal foil tothe solar cell 212 n at step 206. For example, a heated bonding headand/or bonding roller to a predetermined bonding temperatureapproximately in the range of 100-600° C. As another example, thepredetermined bonding temperature can be approximately in the range of350-580° C. Such thermo-compression approaches may be performed toprovide thermo-compression bonding of an aluminum (or other metal) foildirectly to a substrate or wafer of a solar cell. In one embodiment, themetal foil can be coupled to the bottom anti reflective coating (BARC)material or other protective layer (such as a layer amorphous silicon).Additionally, thermo-compression bonding can be employed to bond a metalfoil directly to a sputtered metal seed layer on a substrate or wafer ofa solar cell.

In various embodiment, the ultimate metallization layer for fabricatingelectrical contacts for a solar cell is a metal foil layer, such as analuminum metal foil. A metal foil can be patterned to provide electricalcontacts, metallization structures and/or fingers for underlyingsemiconductor regions of a solar cell. For example, the metal foil 132can be patterned at locations between a plurality of semiconductorregions 113/115 as depicted in FIG. 3B. The metal foil 132 compriseselectrically isolated regions which are metallization structures, eachin electrical contact with alternating semiconductor regions 113/115.

In some embodiments, the metal foil is “pre-patterned” or patternedbefore being coupled to the solar cell wafer such that a metal foilcomprising a pattern of electrically isolated regions is conveyed to thefirst roll unit and aligned with desired regions of the solar cell uponcontact. However, in outer embodiments, the metal foil can be patternedafter being coupled to the wafer of the solar cell.

As used herein, electrical isolation refers to physically separatingportions of a metal foil and/or metal seed layer such that electricalconduction across a groove, indentation and/or trench is not possible oris otherwise impractical. However, metallization structures or fingersmay be connected so as to conduct electrical current through otherpathways, for example electrical conduits like bus bars which can beprovided in any desired configuration.

In some embodiments, the metal foil can be patterned during orsubstantially simultaneously as the step of bonding of the metal foil tothe solar cell at 206. In yet other embodiments, the metal foil can bepatterned at optional step 208 of flowchart 200 in FIG. 4. In oneembodiment, patterning is a continuous process employing a patterningroller unit or a rotary cutting die having a generally curved or arcuatecross-section to isolate metal foil regions to form metallizationstructures on each solar cell and/or trim excess metal foil to defineinterconnects between adjacent solar cells. As additional examples, arotary die, flexible die or rigid planar die is pressed into the metalfoil to form a pattern. In the example depicted in FIG. 5, a patterningroller 260 rolls across solar cell string 350 while applying amechanical force on metal foil 232 of solar cell string 250.

In some embodiments, the patterning roller 260 comprises cutter bladeshaving any desirable shape, size, or configuration. The patterningroller and/or cutter blade(s) of a rotary cutting die can be provided inany desired pattern or configuration to electrically isolate metal foilregions, electrically isolate metal seed regions and/or trim of excessmetal foil during a patterning operations.

The patterning may not necessarily be done prior to the bonding step 206or simultaneously with the bonding step 206. For example, the patterningstep could be a separate screen printing or die cutting step performedon the cell string 250 subsequent to its manufacture.

In an embodiment, the cell string 250 comprises at least a portion ofmetal foil 232 remaining intact between adjacent solar cells 212. Themetal foil 232 spanning between adjacent solar cells 212 can beelectrically conductive interconnects of a solar cell string or module.In some embodiments, the metal foil can be patterned or trimmed atlocations between the solar cells while still maintaining electricallyconductive foil interconnects between cells, for example to providestrain relief elements. In some embodiments, the foil between adjacentsolar cells can be substantially entirely cut after a predeterminednumber of sequential solar cells form a cell string, for example toproduce a plurality of cell strings with each solar cell string being8-16 solar cells long. However, in yet other embodiments whereindividual solar cells are desired, the metal foil can be cut betweeneach solar cell.

At optional step 210 in flowchart 200 of FIG. 4, the method of forming asolar cell string or module comprises passing the plurality of solarcells in a solar cell string through at least one flattening roll unitto induce a flat orientation. In the exemplary embodiment of FIG. 7, thesolar cell string 250 is passed through a third roll unit 270 comprisingtwo rollers 272/274 located on either side of solar cell string 250. Thethird roll unit contacts or presses solar cell string 250 to induce aflat orientation around a first axis 280 parallel to the firstconveyance path 222. Additionally, the solar cell string 250 is passedthrough a fourth large diameter roll unit 276 located on the side of thesolar cell string 250 opposite the metal foil. The fourth roll unitcontacts or presses solar cell string 250 to induce a flat orientationaround a second axis 282 perpendicular to the first conveyance path 222.The solar cell string can be passed through any desirable number offlattening roll units comprising any number of rollers and having anydesirable orientation or size to induce a flat orientation. In variousembodiments, the wafer or solar cell can be characterized by apredetermined curvature substantially equivalent to the curvature of thefirst roll unit.

Not to be bound by any particular theory, but due to non-uniform thermalproperties of the foil and wafer of a solar cell string, heating orannealing operations, e.g. while coupling metal foil and wafer, canresult in a bent or bowed solar cell string during cooling to roomtemperature. Thus, the solar cell string can be passed through anydesirable number of flattening units in any order to induce a flatorientation around any suitable axis. In some embodiments, the solarcell wafers can be by “pre-bent” or “pre-tensioned” in advance ofproviding the solar cell wafers on the first roll unit by applying aforce to deform the wafers into an initial orientation.

Disclosed herein is a solar or photovoltaic module and a method ofmanufacturing thereof. The method of manufacturing a solar modulecomprises a step of providing a plurality of solar cells on a first rollunit configured to maintain the plurality of solar cells in apredetermined cell string arrangement of the solar module. For example,FIG. 8 depicts a solar cell string 350 comprising a plurality of solarcells 312 interconnected by a metal foil 332. The solar cell string 250can be encapsulated by an encapsulant 392 in any desirable cell stringarrangement to form a photovoltaic laminate or module 352. FIG. 9depicts a solar laminate or module 352 comprising a solar cell string350 encapsulated between a superstrate (e.g. glass) 394 and a backsheet396.

The above specification and examples provide a complete description ofthe structure, and use of illustrative embodiments. Although certainembodiments have been described above with a certain degree ofparticularity, or with reference to one or more individual embodiments,those skilled in the art could make numerous alterations to thedisclosed embodiments without departing from the scope of thisinvention. As such, the various illustrative embodiments of the methodsand systems are not intended to be limited to the particular formsdisclosed. Rather, they include all modifications and alternativesfalling within the scope of the claims, and embodiments other than theone shown can include some or all of the features of the depictedembodiment. For example, elements can be omitted or combined as aunitary structure, and/or connections can be substituted. Further, whereappropriate, aspects of any of the examples described above can becombined with aspects of any of the other examples described to formfurther examples having comparable or different properties and/orfunctions, and addressing the same or different problems. Similarly, itwill be understood that the benefits and advantages described above canrelate to one embodiment or can relate to several embodiments. Forexample, embodiments of the present methods and systems can be practicedand/or implemented using different structural configurations, materials,and/or control manufacturing steps. The claims are not intended toinclude, and should not be interpreted to include, means-plus- orstep-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” or “step for,”respectively.

The invention claimed is:
 1. A method of manufacturing a solar cellstring, the method comprising: providing a plurality of solar cells on afirst roll unit rotating along a first conveyance path; each of theplurality of solar cells comprising a front side facing the sun duringnormal operation to collect solar radiation and a back side opposite thefront side; the front sides of the solar cells contacting the first rollunit; wherein each of the plurality of solar cells further comprisesalternating n-type and p-type polycrystalline silicon semiconductorregions on a single crystalline silicon substrate; conveying an aluminumfoil from a second roll unit directly to the first roll unit withoutcontacting the first roll unit, wherein the aluminum foil contacts theback side of the solar cells on the first roll unit along the firstconveyance path; bonding the aluminum foil to the back sides of theplurality of solar cells by applying a mechanical force to a bondinghead directed towards the first roller unit; wherein the plurality ofsolar cells form a solar cell string comprising an aluminum foilinterconnect between each of the plurality of solar cells; patterningthe aluminum foil at locations between the plurality of alternatingn-type and p-type polycrystalline silicon semiconductor regions toelectrically isolate regions of the aluminum foil; passing the solarcell string through a third roll unit, wherein the third roll unitcontacts the solar cell string to induce a flat orientation around afirst axis parallel to the first conveyance path; passing the solar cellstring through a fourth roll unit, wherein the fourth roll unit contactsthe solar cell string to induce a flat orientation around a second axisperpendicular to the first conveyance path.
 2. The method according toclaim 1, further comprising a step of heating the plurality of solarcells, the aluminum foil, or a combination thereof.
 3. A method offabricating a solar cell, the method comprising: providing at least onewafer on a first roll unit; the at least one wafer comprising aplurality of semiconductor regions; conveying a metal foil directly tothe first roll unit without contacting the first roll unit, wherein themetal foil contacts the at least one wafer on the first roll unit;coupling the metal foil to the at least one wafer to provide a unifiedpairing of the metal foil and the at least one wafer.
 4. The methodaccording to claim 3, wherein providing the at least one wafer on thefirst roll unit comprises providing the at least one wafer on the firstroll unit heated to a predetermined temperature.
 5. The method accordingto claim 4, wherein the predetermined temperature is in the range of100-600° C.
 6. The method according to claim 3, further comprising astep of heating the at least one wafer before providing the at least onewafer on the first roll unit, a step of heating the metal foil beforeconveying the metal foil to the first roll unit, or a combinationthereof.
 7. The method according to claim 3, wherein providing at leastone wafer on a first roll unit comprises applying a vacuum suction tohold the at least one wafer on the first roll unit.
 8. The methodaccording to claim 3, wherein conveying a metal foil to the first rollunit comprises conveying an aluminum foil to the first roll unit.
 9. Themethod according to claim 3, wherein coupling the metal foil to the atleast one wafer comprises applying a mechanical force to a bonding headdirected towards the first roller unit.
 10. The method according toclaim 3, wherein coupling the metal foil to the at least one wafercomprises impinging a laser beam on the metal foil to weld the metalfoil to the at least one wafer.
 11. The method according to claim 3,further comprising a step of patterning the metal foil at locationsbetween the plurality of semiconductor regions to electrically isolateregions of the metal foil.
 12. The method according to claim 3, furthercomprising a step of passing the plurality of solar cells through atleast one flattening roll unit to induce a flat orientation.
 13. Themethod according to claim 3, wherein providing at least one wafer on afirst roll unit comprises providing at least one wafer on a first rollunit comprising a plurality of substantially planar surfaces sized tohold a single wafer.
 14. The method according to claim 3, whereinproviding at least one wafer on a first roll unit comprises providing atleast one wafer on a first roll unit having a cylindrical cross-section.15. The method according to claim 3, further comprising a step ofapplying a force to deform the plurality of solar cells into an initialorientation in advance of providing at least one wafer on a first rollunit.
 16. A method of manufacturing a solar module, the methodcomprising: providing a plurality of solar cells on a first roll unitconfigured to maintain the plurality of solar cells in a predeterminedcell string arrangement of a solar module; each of the plurality ofsolar cells comprising a plurality of semiconductor regions; conveying ametal foil directly to the first roll unit without contacting the firstroll unit, wherein the metal foil contacts the plurality of solar cellson the first roll unit; coupling the metal foil to the plurality ofsolar cells to provide a unified pairing of the metal foil and theplurality of solar cells; encapsulating the cell string arrangement toform a photovoltaic laminate.
 17. The method of manufacturing a solarmodule according to claim 16, further comprising the step of patterningthe metal foil at locations between the plurality of semiconductorregions to electrically isolate regions of the metal foil.